1. Field of the Invention
This invention relates to a semiconductor device manufacturing method especially suitable for a method using high-pressure reflow to plug contact-holes and grooves.
2. Description of the Related Art
Along with high integration of very large scaled integrated circuits, micro-sized inside wiring progresses, and the aspect ratio of contact-holes increases. Therefore, technologies for plugging a wiring material into fine contact-holes having a high aspect ratio is very important.
Recently, researches of so-called plugged wiring technologies are done actively. Plugged wiring technologies pertain to a process of forming a predetermined groove in an inter-layer insulation film, then stacking a film of a wiring material, such as aluminum (Al) or copper (Cu), to plug it into the groove, and thereafter removing the wiring material from portions other than the groove by CMP (chemical mechanical polishing), so as to use the remainder of the wiring material in the groove as a wiring. In such plugged wiring technologies, the technique for plugging a wiring material into a fine groove is important.
There are researches of various techniques, such as blanket tungsten (W) chemical vapor deposition, aluminum (Al) or copper (Cu) high-temperature sputtering, reflow, and high-pressure reflow, as techniques for plugging of fine contact-holes and grooves, and some of them are used actually.
Blanket W CVD is most widely used in practice as a technique for plugging of contact-holes because of its high and stable hole-plugging ability. However, its process is complicated, requiring steps of forming a close-contact layer, forming and back-etching the W film and forming a wiring.
Al or Cu high-temperature sputtering and reflow are simpler in process than the blanket W CVD, and hence contributes to a reduction of the cost. However, they need heating the substrate as high as approximately 500 to 550.degree. C. for plugging of contact-holes, and invite a decrease in reliability of the wiring due to heating the substrate to a high temperature, among others. Moreover, high-temperature sputtering and reflow are inferior in plugging ability, and the maximum aspect ratio, in case of contact-holes, for example, is 2 to 3, approximately. Therefore, these methods are considered inapplicable to more micro-sized devices in the future.
Al or Cu high-pressure reflow is recently remarked as a technology improving the plugging ability of the ordinary reflow. The high-pressure reflow ensures plugging of contact-holes with an aspect ratio around 4 to 5 under an ideal condition, and is appreciated as a hopeful method applicable also to plugging of grooves. FIGS. 1 through 3 show a conventional method for manufacturing a semiconductor device by plugging an Al alloy into a contact-hole by the high-pressure reflow.
In the conventional semiconductor device manufacturing method, first formed, as shown in FIG. 1, is an underlying Al alloy wiring 103 made of an Al--Cu alloy on a semiconductor substrate 101, such as Si wafer, prepared by a predetermined process, via an inter-layer insulation film 102, such as SiO.sub.2 film. Next formed on the entire surface is an inter-layer insulation film 104, such as SiO.sub.2 film, by chemical vapor deposition (CVD), for example. Thereafter, a predetermined portion of the inter-layer insulation film 104 is selectively etched off by dry etching to form a contact-hole C' down to the underlying Al alloy wiring 103. Symbols x' and y' are the diameter and the depth of the contact-hole C'. Numerical values of x' and y' may be, for example, x'=0.3.mu.m and y'=1.mu.m.
Next stacked as an underlying wiring layer are a titanium (Ti) film and a titanium nitride (TiN) film, in sequence, by sputtering at the temperature of 400.degree. C. of the semiconductor substrate 101 to form a TiN/Ti film 105. The lower Ti film may be 20 nm thick and the upper TiN film 50 nm thick, for example, such that the entirety of the TiN/Ti film 105 be 70 nm thick. Next formed on the TiN/Ti film 105 is an Al alloy film 106, using an Al--Cu alloy, for example, as a wiring main material by sputtering at the temperature of, for example, 400.degree. C. of the semiconductor substrate 101. The thickness of the Al alloy film 106 is chosen to be larger than the diameter x' of the contact-hole C', so as to cover the upper end of the contact-hole C' while making a void inside the contact-hole C'. For example, thickness of the Al alloy film 106 may be 500 nm.
After the Al alloy film 106 is formed, as shown in FIG. 2, the semiconductor substrate 101 is heated to 400 to 450.degree. C. in a highly evacuated atmosphere to soften the Al alloy film 106, and a pressurized gas is introduced to make the Al alloy film 106 run into the contact-hole C' until it fully plugs the contact-hole C' as shown in FIG. 3.
In the conventional semiconductor device manufacturing method, successive steps of forming the TiN/Ti film 105, forming the Al alloy film 106 and high-pressure reflow of the Al alloy film 106 are executed continuously while transporting the semiconductor substrate 101 in a vacuum not to expose it to the atmospheric air.
In the conventional semiconductor device manufacturing method, the plugging ratio of the contact-hole or groove by the high-pressure reflow is very sensitive to the quality of the inter-layer insulation film 104 having the contact-hole or groove. Especially when a large amount of gases of water, etc., are released from the surface of the inter-layer insulation film 104, the plugging ratio decreases seriously. The problem of a gas released from the inter-layer insulation film 104 may occur, for example, in the following case. That is, as the requirement of a flatness of the underlying surface making a wiring increases along with micro-sizing and multi-layered wiring of VLSIs, insulation films excellent in flatness tend to be used frequently. More specifically, the above-explained conventional semiconductor device manufacturing method may use an insulation film with an excellent flatness to flush a step by the underlying Al alloy wiring 103. A known film usable as the insulation film for this purpose is, for example, a SiO.sub.2 film formed by atmospheric-pressure CVD using ozone (O.sub.3) and tetraethoxysilane (TEOS) as reactive gases. Such a SiO.sub.2 film is certainly good in flatness. However, it is highly hygroscopic, and contains much moisture. If the inter-layer insulation film 104 includes a much moist portion, even when the much moist portion is not exposed to the exterior, water, etc., are released to the exterior through the inter-layer insulation film 104, and degrades the plugging ratio.
This occurs for the following reason. That is, in the conventional semiconductor device manufacturing method referred to above, a sequence of steps of forming the TiN/Ti film 105, forming the Al alloy film 106, and high-pressure reflow of the Al alloy film 106 are executed together with heating of the semiconductor substrate 101 around 400 to 450.degree. C., and gases of water, etc., are released from the inter-layer insulation film 104. Since the gases of water, etc. released from the inter-layer insulation film 104 pass through the TiN/Ti film 105 forming the side wall of the contact-hole C', water molecules reach the surface of the TiN/Ti film 105. As a result, as shown in FIG. 4, the surface of the TiN/Ti film 105 is oxidized, and a Ti oxide layer 108 is formed the portion. Once the Ti oxide layer 108 is formed on the surface of the TiN/Ti film 105, the Al alloy film 106 is oxidized along the interface with the TiN/Ti film 105 as shown in FIG. 5 when the Al alloy film 106 runs into the contact-hole C' during high-pressure reflow, and an Al oxide layer 109, such as aluminum dioxide (Al.sub.2 O.sub.3) in the portion. The Al oxide layer 109 does not run smoothly, and disturbs the reflow of the Al alloy film 106. Supposedly, this is the reason of defective plugging.
This problem is salient when a wiring material is plugged into a micro-sized contact-hole or groove by high-pressure reflow, causing a decrease in reliability of the wiring and an increase of the wiring resistance due to the defective plugging. Therefore, there is a demand for an improved measure that ensures good plugging regardless of the quality of the inter-layer insulation film 104.